Firelighter composition in gelled form which solidifies upon ignition

ABSTRACT

A firelighter composition is a jelly or paste but upon ignition it solidifies, at least at its surface. The composition comprises a dispersion of an organic fuel in a liquid vehicle comprising a polymerisable material that polymerises upon ignition.

United States Patent Tanner Apr. 2, 1974 [54] FIRELIGIITER COMPOSITIONIN GELLED [56] References Cited FORM WHICH SOLIDIFIES UPON ED STATESPATENTS IGNITION 3,615,286 10/1971 Vander Linden 44 7 D [75] Inventor:David J. Tanner, Larkhall, Scotland FOREIGN PATENTS OR APPLICATIONSAssigneei y Manufacturing Company 945,439 12/1963 Great Britain 44 7 RLimi d, Ea Ki ri g g 962,678 7/1964 Great Britain 44/7 R Scotland Filed:Apr. 6, 1972 App]. No.: 241,797

Foreign Application Priority Data Primary Examiner-Benjamin R. PadgettAttorney, Agent, or Firm-Lawrence Rosen; E. Janet Berry [57] ABSTRACT Afirelighter composition is a jelly or paste but upon ignition itsolidifies, at least at its surface. The composition comprises adispersion of an organic fuel in a liquid vehicle comprising apolymerisable material that polymerises upon ignition.

19 Claims, No Drawings FIRELIGHTER COMPOSITION IN GELLED FORM WHICHSOLIDIFIES UPON IGNITION It is well known to make firelightercompositions based on an organic liquid fuel. Usually the compositionsare manufacture by shaping a liquid system into block form andsolidifying it in that form. For many reasons it would be more desirableto use the composition in fluid form, i.e. a form in which it can beextruded or otherwise made to flow. Thus it would avoid the necessity offorming blocks of unit size, would simplify packaging, would permit theuser to select more easily the amount of composition that he wanted forany particular occasion, would permit the user to dispense thecomposition into position without having to handle it and wouldfacilitate ensuring intimate contact between the fuel to be ignited andthe composition.

The use of a liquid firelighter has, so far, been unsatisfactory. Thuswith most liquid compositions consisting of or containing an organicliquid fuel there is a serious risk of flash back occurring. Further,most liquid compositions of an organic liquid fuel burn very fast andthus may not serve as good ignition agents.

In an attempt at minimising flash-back it has been proposed to fonnulatea firelighter composition in the form of a paste by compounding theorganic liquid fuel with a sufficient amount of a thickening agent. Inpractice this severely limits the liquids that can be used and generallythe liquid has to be an alcohol. This is undesirable since paraffinswould otherwise generally be preferred as the liquidsince alcohols aremore expensive, are more volatile and have lower flashpoint, and thustheir use in the large quantities that are required as the fuel is verymich more expensive and is more hazardous. Also the use of largequantities of alcohols can present a toxicity problem.

Even apart from the disadvantages of being effectively limited to theuse of alcohols as the fuel, the known pastes are not very satisfactorysince the liquid fuel does, in practice, flow or spatter during burningand may, for example, flow over the hearth ofa domestic fireplace. Alsothe paste burns rapidly and so is not very efficient as a firelighter.

According to the invention a firelighter composition is provided in theform of apaste or jelly comprising a dispersion of an organic fuel in aliquid vehicle comprising a polymerisable material and in which, uponignition, the polymerisable material polymerises and the composition issolidified, at least at its surface. It is sufficient if solidificationoccurs only at the surface to form a skin of adequate strength toprevent the composition flowing or spattering and to prevent excessiveweepage of the fuel. Often, however, all the composition, or at leastsubstantially all the composition, solidifies upon ignition.

Because the fuel is dispersed in the liquid, which usually compriseswater, and because the composition does not flow on ignition paraffinscan be used as the liquid fuel, the hazards of using a flowablecomposition are eliminated or reduced, and the composition burns moreslowly and is thus more effective as an ignition agent. The organic fuelusually consists solely of a liquid but solid material, for exampleparaffin wax, may in some instances be used in place of all or part ofthe liquid fuel.

Part at least of the solidification that occurs is due to thepolymerisation of the polymerisable material, and

this polymerisation preferably results in the formation of a solidmatrix in which the fuel is dispersed.

The polymerisable material is preferably a formaldehyde resin, and mostspecially a carbamide resin, the preferred material being a ureaformaldehyde resin. We are using the term resin in this context in theusual sense when referring to polymerisable formaldehyde and carbamideresins, i.e. to denote a material that is capable of forming a polymerbut which may itself be of very low molecular weight, or may be highermolecular weight polymer.

The composition may include a single ingredient that will polymeriseupon heating, for example a self-crosslinkable resin, e.g. a fairly highmolecular weight resin that cures merely on heating. Often however thecomposition includes two or more ingredients that will give rise to thedesired reaction upon ignition.

Each of these ingredients may be present in the form in which it is toeffect the reaction, the composition thus merely requiring sufficientheating to bring about reaction, but more usually at least one of theingredients is in a form in which it is incapable of reacting with theother ingredient until it is chemically or physically released as aresult of heating. Thus it may be in the form of a compound from whichit is liberated during heating, or it may be encapsulated within amaterial that disintegrates on heating, for example a thermoplasticmaterial, or it may be in the form of a precursor compound that willreact upon ignition with another compound.

The degree of heating necessary to bring about the reaction must not bemore than that which occurs upon ignition of the composition, andpreferably is rather less. For example reaction is preferably broughtabout at temperatures as low as C. Preferably, however,

reaction does not occur at very low temperatures, for

example below 30C and preferably not below 50C, as otherwise thestability of the composition on storage may be impaired.

One of the reactive ingredients for the reaction will be a polymerisablemonomer or polymer and the other may be a catalyst for effecting thepolymerisation or may be a copolymerisable monomer. For example thecomposition may comprise, as one ingredient, a polymerisable monomer orpolymer and, as the other ingredient, encapsulated copolymerisablemonomer or low molecular weight polymer, the encapsulating materialbeing of a suitable thermoplastic material.

In another composition one ingredient is a polymerisable monomer orpolymer while the second ingredient is a catalyst for thepolymerisationof this monomer or polymer, or a material from which such a catalyst isliberated during heating. The second ingredient may thus comprise thecatalyst encapsulated within a suitable thermoplastic material. Inanother system it may comprise a compound that liberates the catalyst onheating. For example if the polymerisation of the polymerisable materialis catalysed by an acidic catalyst the ingredient may be a nitrate whichwill liberate acidic nitrogen oxides on heating or epichlorhydrin whichliberates hydrochloric acid on heating.

In another system the second ingredient may be a catalyst for thepolymerisation of the first ingredient but which has been inactivated byreaction with a volatile material. For example the catalyst may be anacidic catalyst which has been inactivated by reaction with a volatilebase, for example triethylamine. Upon ignition the volatile base flashesoff and thereby liberates the acidic catalyst. A good method of usingthis system is to use a urea formaldehyde resin which has beenneutralised during manufacture with for example triethylamine. Thisgives a resin which becomes acidic on heatmg.

A wide variety of other acid liberating compounds or other compoundsthat will liberate suitable polymerisation catalysts can be used.

In yet another system the first ingredient is a formaldehyde resin andthe second is a material that reacts with formaldehyde that is liberatedfrom the resin on heating to generate a catalyst. Most formaldehyderesins liberate formaldehyde rapidly on heating at 80l00C. The secondingredient may thus be an ammonium salt, since this will generate anacid on reaction with formaldehyde. Suitable salts include partiallysoluble salts, for example diammonium hydrogen phosphate, or sparinglysoluble salts. However, most ammonium salts will provide the necessaryreaction and the preferred salts are ammonium chloride, diammonium andtriammonium phosphate, ammonium sulphate, ammonium nitrate and ammoniumformate or citrate. To prevent reaction before heating free formaldehydein the resin may be taken up by inclusion in the past of, for example,free urea or ammonia. This may tend to break the emulsion but thistendency can be overcome by increasing the viscosity of the paste and/orby increasing the content of stabiliser in the paste. Instead of ammoniaor urea other compounds having very reactive amine or amide groups maybe used to react with the free formaldehyde. The liberation offormaldehyde is an equilibrium reaction and preferably the amide oramide is added to the formaldehyde resin at least 24 hours before thesalt is added, in order to ensure that equilibrium between the resin andformaldehyde, and therefore complete reaction of all the formaldehydewith amine or amide, has been achieved before the salt is added.

An alternative way of preventing premature liberation of formaldehydeand thus reaction of the resin is to include in the aqueous system abuffering agent capable of maintaining the paste at a pH of from 6.5 to8.5. Suitable buffering agents are strong base weak acid compounds, forexample sodium acetate.

In yet another system one ingredient is a hydrolysable esteror'anhydride that, upon hydrolysis, will polymerise and/or liberate afree acid. This system may include a material that will catalyse thishydrolysis at elevated temperatures e.g. thermosensitive hydrolysissynergists.

If one of the ingredients comprises an encapsulated material thecapsules should have a density similar to that of the emulsion. Forexample the encapsulent may be chosen to have the appropriate density.Suitable encapsulents include partially expanded polystyrene,polyurethane, polypropylene or nylon. Naturally thermoplasticencapsulents will be chosen, for example by appropriate selection of themolecular weight, to have a melting point such that the encapsulatedmaterial is liberated at the appropriate temperature.

The compositions of the invention preferablycontain, as one ingredient,a partially condensed carbamide resin and, as the other ingredient,encapsulated acidic catalyst or a material that liberates acidiccatalyst on heating. Suitable partially condensed resins are the ureaformaldehyde, melamine formaldehyde and 'dicyandiamide formaldehydepolymers, the urea formaldehyde polymers generally being preferred. Thedegree of condensation is preferably fairly well advanced in order thatsolidification of the composition occurs rapidly once the appropriatetemperature is reached. However even urea formaldehyde resins havingonly a low degree of condensation can satisfactorily be used.

The liquid vehicle is usually an aqueous vehicle,

water constituting all or most of the solvent in the vehicle. Thus thevehicle usually consists essentially of the polymerisable material inwater, the polymerisable material usually being in solution in water.However nonaqueous liquids can be included. For example some or all ofthe water may be replaced by a volatile organic solvent. This canpromote solidification. For example if the liquid vehicle contains apolymerisable monomer or low molecular weight polymer, for example asolution of a partially polymerised but stabilised formaldehyde resin,upon increasing the concentration of the resin in the solution, byremoving part of the solvent, further polymerisation of the resin can beinitiated and the composition thereby converted to solid form. Usually,however, if volatile organic solvent is present it is present incombination with water, the water usually being present in the largeramount. Suitable amounts of volatile solvent are 0.1 to 0.5 percent byweight based on the total weight of paste. Volatile organic liquids thatcan be used are ones that boil below C. The preferred organic liquidsare alcohols. Suitable alcohols are methyl alcohol, ethyl alcohol, butylalcohol, propyl alcohol, amyl alcohol and isoamyl alcohol.

The compositions of the invention are either pastes or jellies. Thusthey are fluid, in the sense that they can be extruded, but they maynevertheless have a fairly firm consistency. If they are jellies thenthey would be meltable, i.e. upon heating they would tend to melt, butfor the fact that polymerisation and solidification occurs, at least atthe surface. Some melting may occur before polymerisation is completed.The jellies offer the advantage that when the composition is'extruded,for use, through the orifice of a suitable dispenser the surface of thejelly is torn by attrition at the orifice and this torn surface resultsin some free hydrocarbon fuel at the surface. As a result initialignition of the paste is very easy. Further, the jelly does not readilybreak down upon ignition and-so burning time is prolonged and the flameheight is low, with the result that maximum use is made of the heat thatis generated.

The resin used and the amounts of water and fuel present are often suchthat the dispersion of fuel in aqueous resin is a paste. However it isoften desirable to include in the composition various thickeners, bothto give the composition paste, or an improved, paste consistency or ajelly consistency and also to improve the characteristics of thecomposition upon ignition. These thickeners may themselves act asstabilisers for the dispersion but, in addition, surfactants may beincluded to act as stabilisers. The amount of surfactant is usually from0.3 to 1.5 percent by volume. Suitable surfactants are the neutralsodium benzene sulphonates, a preferred material being sodium dodecylbenzene sulphonate. However a wide variety of other surfactants can beused, for example various surfactants containing fluorine, such as therange known as Fluorochemicals, e.g. the material sold by l.C.l. as PC123, and the sulpho succinate surfactants The amount of stabiliser thatis included can vary over a wide range depending partly upon thematerial that is used and partly upon whether it is present solely tothicken and stabilise the paste dispersion or whether it is present alsoto improve the properties of the paste upon ignition. Usually, however,the amount is from 0.01 to 5 percent by weight based on the paste, mostusually from 0.1 to 3 percent and preferably from 0.1 to 1 percent. v

Suitable stabilisers are the materials that are often known asprotective colloids. Preferred stabilisers are long chain water solubleorganic chemicals having many functional groups, for example carboxylic,amino or hydroxyl groups. Such stabilisers exhibit a high de gree ofhydrogen bonding and/or they complex to form a colloidal gel. They actas powerful emulsion stabilisers and prevent breakdown of the emulsioneven under adverse temperature conditions. In general they also arechemicals which burn more slowly than the kerosene or other liquid fueland they tend to char. Thus they act as a reinforcing agent for thegelled polymer skin during burning of the composition.

Cellulosic material can be used as stabiliser. Thus the water caninclude materials such as hydroxymethyl cellulose and carboxymethylcellulose. These materials not only increase the viscosity of the paste,give it long term storage stability and stabilise it against breakdownupon freezing and thawing but also they result in the formation of acarbonaceous structure upon ignition. This carbonaceous structure burnsslowly, usually more slowly than the fuel that is dispersed in thepaste, and so the burning time of the composition is extended. Forexample upon evaporation of the water or other solvent .when the pasteis ignited a porous structure of charcoal may be formed eitherthroughout the body of the paste or at least at the surface of thepaste. The porous structure is reinforced by the polymerised material.

Other stabilisers that can be used, and which perform a similar functionto the cellulose stabilisers, are the alginates and caseinates,forexample sodium, potassium or calcium alginate or caseinate. They may bedefined as long chain organic acid salts derived from seaweed or milkrespectively. They tend to have agreater thickening effect and to'resultin the production of a thicker skin than cellulosic materials.

Another stabiliser that can be used is polyvinyl alcohol which ispreferably partially soluble in water. Thus it may be a partiallyhydrolysed product of low to medium molecular weight. Conveniently it isused as an aqueous emulsion. While it is preferred to use cellulose oralginate stabilisers in amounts of from 0.1 to l percent by weight ofthe paste p.v.a. can be used in greater amounts, for example 0.5 to 5percent, and most preferably about 1 percent by weight of the pastep.v.a. can be used in greater amounts, for example 0.5 to 5 percent, andmost preferably about 1 percent by weight of the paste. Polyvinylalcohol emulsions of medium to high molecular weight form a jellystructure and are thus also useful additives.

Another stabiliser that can be used is gelatin. This is generally usedin an amount of from 0.1 to 5.0 percent by weight. This gives a verygood jelly structure to the composition.

The stabiliser may be a material that reacts chemically upon ignition toincrease the viscosity of the composition, and often to render itsubstantially solid. For example if partially hydrolysed starch isdispersed in the aqueous liquid vehicle upon ignition rapid hydrolysisof the starch occurs and the composition will be converted to acolloidal gel that does not flow. When starch is present it is preferredthat there should be a source of formaldehyde in the paste since thestarch will then react with formaldehyde and become insolubilised, andthis reduces the rate of burning. Usually the polymerisable material isa formaldehyde resin and this will serve as an adequate source offormaldehyde for this purpose.

The fuel that is dispersed in the liquid vehicle may be solid, e.g.naphthalene, but is usually liquid that is emulsified in the vehicle. Avariety of organic liquids, such as oils and ketones, can be used butpreferably the fuel is a hydrocarbon,usually a paraffin cut obtained bydistillation of crude oil. Preferred fuels are paraffin, kerosene or gasoil. The hydrocarbons used are liquid at room temperature and usuallyboil above 150C, for example boiling between 150 and 300C. The amount offuel in the paste is usually between and 97 per cent preferably -95percent, by volume.

The amount of polymerisable material in the composition may be from, forexample, 0.8 to 10 percent by volume. If the composition contains littleor no stabiliser that contributes to solidification upon ignition, forexample if it contains little or none of any of the stabilisersdiscussed above, the amount of polymerisable material will usually befrom 5 to 7.5 percent by volume, and the amount of fuel dispersed in theliquid vehicle will usually be from 80 to percent by volume, the balancebeing water or other solvent. However by the' inclusion of appropriateamounts of appropriate stabilisers it is possible to reduce the amountof polymerisable material to, for example, 0.8 to 5 percent, preferably1 to 3 percent by volume, in which event the amount of hydrocarbon fuelcan be higher, for example 90 to 97 percent and usually 90 to percent byvolume.

The composition may be made by forming an emulsion of the fuel in theliquid vehicle that contains polymerisable material by conventionalmethods, and before or after forming the emulsion stabilisers,surfactants and any other desired additives are included. Thusstabiliser can be added to the liquid vehicle before the fuel isemulsified into it or after. Preferably the emulsion is converted to avery fine cell size by passing the emulsion through a suitableemulsifier, such as a Hobart Paddle Mixer or a Herbort Homogeniser.Preferably the majority of the cells of the emulsion are less than 4microns in size. For example at least 65 percent of the cells may havecell size from 1 to 4 microns with the rest 5 to 20 microns.

The composition preferably has a viscosity of 500 to 1,000 poisealthough any viscosity such that the composition has a jelly paste-likeconsistency can be used.

It is sometimes desirable to disperse additional liquid hydrocarbon orother fuel into the composition after the fuel-in-water dispersion hasbeen formed. This is particularly desirable when the composition is ajelly.

The composition is most conveniently packaged in a dispenser from whichis can be extruded by compression. For example it may be packaged in atube having one end permanently closed and an openable orifice at theother end.

The following are some examples of the invention. The composition madein each of these examples may be packed in a tube having flexible wallsand having an openable outlet at one end. Upon being dispensed the pastesolidifies and burns slowly without flashback. The composition ofExample 1 was satisfactory but did solidify rather more slowly than thecompositions of the other Examples and was not so storage stable as manyof the others, especially those containing stabilisers. Example 1 5.12Parts by volume of a 66 percent by weight solids aqueous solution ofpartially condensed urea formaldehyde (sold under the Trade Name CascoUL 46) was mixed with 3.42 parts by volume of water, 0.40 parts byvolume of a 30 percent aqueous solution of sodium dodecyl benzenesulphonate (sold under the Trade Name Arylan SBC 425) and over a periodof 10 minutes 91.06 parts by weight of commercial grade kerosene wasadded slowly and emulsified into the mixture by mixing. The paste wasthen passed through a Herbort Homogeniser to produce a cell size of 4microns or less. The resultant paste was termed paste A.

Urea formaldehyde resin Casco UL 46 is a moderately high molecularweight resin that polymerises on sufficient heating. It is believed tobe a resin that was produced by acid catalysis and in which thecondensation has been stopped by the addition of sodium hydroxide.

Example 2 0.5 Parts by volume of microencapsulated phosphoric acid, inwhich the encapsulated material is 85 percent phosphoric acid and theencapsulating material low molecular weight nylon, are mixed by a simplepaddle mixer with 100 parts by volume of paste A. Example 3 0.5 Volumesof triethylamine hydrochloride are mixed by a paddle mixer with 100volumes of paste A.

A product similar to the one obtained by adding triethylaminehydrochloride to paste A is obtained by forming the paste initially froma urea formaldehyde resin neutralised with triethylamine.

Example 4 i 100 Parts by volume of paste A are mixed with from 0.25 to0.3 parts by volume of 0.880 ammonia. After standing for 16 to 24 hours0.5 to 1.0 parts by volume of 10 percent diammonium hydrogen phosphatesolution are mixed into the resultant paste.

In an alternative process the ammonia can be omitted and 0.25 to 0.3parts by weight urea used instead. Example 5 100 Parts by volume ofpaste A are mixed with 0.02 to 0.1 parts by weight sodium acetate.Thereafter 0.5 to 1 parts by weight of percent ammonium chloride aqueoussolution are mixed into the paste.

Example 6 A paste similar to that in Example 1 but which solidifies morequickly is prepared by the same process as is described in Example 1 andfrom the same materials except that instead of using 3.42 parts waterthere is used 2.42 parts by volume water and 1.0 parts by volume ethylalcohol.

Example 7 A stabiliser solution is made by dissolving 25 gramscarboxymethyl cellulose into 440 mls warm water. 3.2 Volumes of thissolution are then mixed by paddle mixer with volumes of paste A togetherwith 0.5

Inplace of alginate there may be used, in a similar manner, caseinproducts such as the calcium salt of casein. There may also be used, forexample, potassium or sodium compounds in place of the calcium compoundsmentioned. The corresponding ammonium compounds may also be used, but isis then preferred to include also ammonia, urea or sodium acetate, as inExamples 4 and 5.

Example 9 100 Volumes of paste A may be blended by paddle mixer with 0.5volumes triethylamine hydrochloride and 3 volumes of a 50 percentsolidspolyvinyl alcohol emulsion to form a jelly. When lower amounts, e.g.down to 1 volume, of p.v.a. are'used a paste is formed while at higheramounts, e.g. up to- 8 volumes, a dry jelly is obtained.

Example 10 0.22 Grams technical grade gelatin are dissolved in 2.2 mlshot water and are then mixed into 100 mls of paste A. Before cooling theresultant paste is extruded into suitable tubes. On cooling the productbecomes a soft jelly which can readily be extruded from its tube andignites quickly. Example 11 The process of Example 10 is repeated exceptthat after the gelatin solution has been mixed into the paste 44 mlskerosene are mixed into the resultant paste over a period of 2 minutes.

Example 12 0.47 Grams gelatin are dissolved in 8.6 mls hot water andthis solution is then mixed into 100 mls of paste A. 100 mls of paraffinare then mixed into the paste over a period of 2 minutes.

In another example the same process is repeated except that the amountof water used for forming the gelatin solution is 17.6 mls and theamount of paraffin used is 56.8 mls.

The products of Examples 10, 11 and 12 are each, on Cooling, softjellies. Example 13 In this example gelatin is used as thickener for apaste, without forming a jelly. Thus 0.12 grams gelatin are dissolved in2.2 mls hot water and the gelatin solution is then mixed into paste A.The product remains as a paste even after cooling. Example 14 2.4 Gramsof starch, for example the material (sold under the Trade Names StadexSE 503 or 777) are mixed thoroughly into 1,000 mls of paste A. Example15 3 Volumes of the carboxymethyl cellulose solution formed in Example 7or the gelatin solution formed in Example are mixed thoroughly by paddlemixer into 100 volumes of paste A. 0.25 To 0.3 volumes of 0.880 ammoniaand 0.5 to 1 volumes 10 percent ammonium chloride solution are thenadded and mixed into the resultant composition. Example 16 3 Volumes ofthe carboxymethyl cellulose solution of Example 7 or of the gelatinsolution of Example 10 are mixed thoroughly into 100 volumes of paste Aand then between 3 and 6 volumes of the alginate solution formed inExample 10 are mixed into the resultant product.

1 claim:

1. A firelighter composition having the form ofa jelly of a paste andcomprising a dispersion of an organic fuel comprising liquid hydrocarbonfuel in a liquid vehicle comprising a polymerisable material comprisinga formaldehyde resin and a catalyst for the polymeriza tion of theformaldehyde resin or a material from which such catalyst is liberatedon heating, and wherein the composition contains at least one heatsensitive ingredient that will react substantially only upon ignition ofthe composition such that the polymerisable material polymerizes and thecomposition is solidified, at least at its surface.

2. A composition according to claim 1 in which the fuel is kerosene.

3. A composition according to claim 1 in which the polymerisablematerial comprises a urea formaldehyde resin.

4. A composition according to claim 1 which includes a catalyst for thepolymerisation encapsulated within a thermoplastic material from whichit is liberated upon ignition.

5. A composition according to claim 1 in which the composition includesa material that reacts with formaldehyde liberated from the resin onignition to form a catalyst for polymerisation of the resin.

6. A composition according to claim 1 in which the composition includesan ammonium salt.

7. A composition according to claim 1 in which the paste includes astabiliser.

8. A composition according to claim 1 in which the paste includes, as astabiliser, a cellulosic compound.

9. A composition according to claim 1 which includes an acidic catalystfor the polymerisation which is present in a form in which it isneutralised by a volatile base.

10. A composition according according claim 1 and which includes an acidpolymerised urea formaldehyde resin neutralised by a volatile base.

11. A composition according to claim 1 in which the composition includesan amine or amide that will react with free formaldehyde to form apolymer.

12. A composition according to claim 1 in which the composition includesammonia or urea.

13. A composition according to claim 1 in which the composition includesa buffering agent capable of maintaining the composition at a pH of from6.5 to 8.5.

liquid vehicle is aqueous.

l which inl which inl which in- 1 which in-

2. A composition according to claim 1 in which the fuel is kerosene. 3.A composition according to claim 1 in which the polymerisable materialcomprises a urea formaldehyde resin.
 4. A composition according to claim1 which includes a catalyst for the polymerisation encapsulated within athermoplastic material from which it is liberated upon ignition.
 5. Acomposition according to claim 1 in which the composition includes amaterial that reacts with formaldehyde liberated from the resin onignition to form a catalyst for polymerisation of the resin.
 6. Acomposition according to claim 1 in which the composition includes anammonium salt.
 7. A composition according to claim 1 in which the pasteincludes a stabiliser.
 8. A composition according to claim 1 in whichthe paste includes, as a stabiliser, a cellulosic compound.
 9. Acomposition according to claim 1 which includes an acidic catalyst forthe polymerisation which is present in a form in which it is neutralisedby a volatile base.
 10. A composition according according claim 1 andwhich includes an acid polymerised urea formaldehyde resin neutralisedby a volatile base.
 11. A composition according to claim 1 in which thecomposition includes an amine or amide that will react with freeformaldehyde to form a polymer.
 12. A composition according to claim 1in which the composition includes ammonia or urea.
 13. A compositionaccording to claim 1 in which the composition includes a buffering agentcapable of maintaining the composition at a pH of from 6.5 to 8.5.
 14. Acomposition according to claim 1 in which the paste includes a volatilealcohol.
 15. A composition according to claim 1 which includes, as astabiliser, a starch.
 16. A composition according to claim 1 whichincludes, as a stabiliser, an alginate.
 17. A composition according toclaim 1 which includes, as a stabiliser, polyvinyl alcohol.
 18. Acomposition according to claim 1 which includes, as a stabiliser,gelatin.
 19. A composition according to claim 1 in which the liquidvehicle is aqueous.